1. Field of the Invention
The present invention relates, in general, to instrumented capsules for nuclear fuel irradiation tests in research reactors and, more particularly, to an instrumented capsule for nuclear fuel irradiation tests in research reactors, which is used to measure in real time the properties of nuclear fuels irradiated in a research reactor during a nuclear fuel irradiation test, thus providing nuclear fuel irradiation test data required for the design of nuclear fuels and the determination of in-pile performance and structural integrity of nuclear fuels.
2. Description of the Related Art
In the related art, nuclear fuel irradiation tests and material irradiation tests in research reactors have been actively executed using irradiation testing facilities, such as capsules or loops. Of the irradiation testing facilities, the capsules which are in-pile testing facilities used in research reactors to execute nuclear fuel irradiation tests are classified into instrumented capsules and non-instrumented capsules. The instrumented capsules are testing facilities in which a variety of measuring instruments are installed in the shell of a capsule to measure the properties of irradiated nuclear fuel, such as the temperature of the irradiated nuclear fuel and the inner pressure and strain of irradiated nuclear fuel rods, and determine in-capsule irradiation test data, such as the quantity of neutron radiation and the temperature, flow quantity and flow rate of coolant. In the meantime, the non-instrumented capsules are testing facilities, the shells of which are not provided with such measuring instruments.
In recent years, the irradiation tests for nuclear reactor materials, nuclear fuels and other nuclear materials by the use of research reactors have been actively studied and executed. Particularly, the requirements for irradiation tests using research reactors have rapidly increased to provide: in-pile irradiation test data for pressure vessels and in-core materials of nuclear reactors in an effort to lengthen the life spans of commercial reactors; in-pile irradiation test data for in-core materials and pressure pipe materials of heavy water reactors in an effort to develop advanced materials for the reactors; and in-pile irradiation test data required for the development of advanced nuclear fuels for pressurized light water reactors, proliferation-resistant oxide nuclear fuels, nuclear fuels for next generation reactors and advanced sheath materials. Thus, a variety of irradiation test facilities which are thermohydraulically and mechanically compatible with in-core irradiation holes of research reactors and agreeable with irradiation test properties of materials have been developed and utilized. In addition, to provide further improved irradiation test facilities, many improvements to the facilities have been attempted.
To provide in-pile test data for design and performance qualification of nuclear fuels for commercial nuclear power plants and in-pile test data for qualifying in-pile performance and structural integrity of nuclear fuels to develop advanced nuclear fuels suitable for a variety of nuclear reactors, such as next generation reactors, irradiation tests using research reactors must be carried out.
To execute the irradiation tests in the research reactors, the non-instrumented capsules and instrumented capsules for the irradiation tests are installed in the irradiation holes of the research reactors to qualify in real time the properties of a variety of nuclear fuels, such as metal fuels and ceramic fuels, during the irradiation tests. In such a case, the capsules must be designed to be thermohydraulically and mechanically compatible with the irradiation holes. Furthermore, the capsules must be prevented from causing mechanical damage to the inner surfaces of the irradiation holes due to in-pile liquid vibration despite being installed in the irradiation holes for lengthy periods. In addition, the capsules must exhibit desired structural integrity and operational reliability thereof even though the capsules are irradiated in the research reactors for lengthy periods. Furthermore, the capsules must be constructed to allow the in-capsule instruments, nuclear fuel rods, fuel rod assemblies, and capsule shells to be easily assembled and disassembled through remote controls from hot cells.
An example of conventional non-instrumented capsules for nuclear fuel irradiation tests may be referred to Korean Patent Registration No. 296946, entitled “Remote-controlled Non-instrumented Capsule for Nuclear Fuel Irradiation Tests”. The above-mentioned non-instrumented capsule can be used in a nuclear fuel irradiation test for a short period, three months to six months, while testing three kinds of sintered nuclear fuels at the same time.
However, the use of the non-instrumented capsule of No. 296946 is limited to an irradiation test for one nuclear fuel rod assembly having three irradiation test fuel rods. Furthermore, the non-instrumented capsule is problematic in that the capsule has a weak welded structure so that some welded parts thereof, such as a collar welded to a rod tip provided at a lower portion of the capsule, may be broken if excessive force is imposed on the welded parts during a process of assembling the capsule. In addition, the capsule is not able to resist wear or breakage induced by in-pile liquid vibration, and furthermore, may damage the inner wall of the irradiation hole caused by the wear.
Furthermore, the above-mentioned non-instrumented capsule is unable to accommodate irradiation growth of structural materials of nuclear fuels, such as sheath materials of fuel rods, induced by lengthy period neutron irradiation, so that the capsule is limited in terms of structural integrity and safety thereof in the irradiation hole when the capsule is used in a nuclear fuel irradiation test for a lengthy period, six months to three years.
Another example of conventional non-instrumented capsules for nuclear fuel irradiation tests may be referred to Korean Patent Application No. 2001-81880, entitled “Non-instrumented Capsule for Nuclear Fuel Irradiation Tests in Irradiation Holes of Research Reactors”. This non-instrumented capsule was developed to solve the problems experienced in the capsule of No. 296946, and has many advantages as follows. That is, the non-instrumented capsule of No. 2001-81880 enhances its structural integrity and safety, thus solving the conventional problems in that the capsule may be easily worn or broken due to external force imposed thereon during the process of assembling the capsule or due to the in-pile liquid vibration. Furthermore, the capsule of No. 2001-81880 has a structure capable of accommodating irradiation growth of fuel rods, thus being effectively used in a lengthy irradiation test. In addition, the capsule includes a thermo-neutron absorption tube capable of allowing for control of linear power density of the nuclear fuel in the irradiation hole.
However, the non-instrumented capsule of No. 2001-81880 having the above-mentioned advantages is problematic in that the capsule does not allow for real time measurement of the properties of the nuclear fuels irradiated in the irradiation hole during an irradiation test.